It is the purpose to: a) determine the hydrolic pressure distribution at several capillary and precapillary vascular segments to venous pressure elevation, and describe transmural pressure values accompanying elicitation of resonse of arterioles and the sphincters. b) Further extend observation and measurement of the microcirculation response to electrical stimulation of selected vasoactive sites of the C.N.S. and medula, and examine interaction, agonistic or antagonistic, of selected naturally occurring biogenic and mediators with neurotransmitter (s). c) the observation and measurement of vessel geometric variables, i.e., diameter of lumen and wall, and area in cross-section, as well as response characteristics to selected vasoactive chemicals will be extended in spontaneously hypertensive rats (SHR). d) examine whether the microvasculature of antibiotic germfree rats and mice also would exhibit refractomines to selected vasoactive drugs. e) the microvascular and microcirculatory resonse to currently used general anesthetics, e.g., ketamine, pentobarbital sodium, halothane and methoxyflurane will be studied.